1. Field of the Invention
This invention relates to a method for soldering aluminum or aluminum alloys, and also to a solder useful in such a method. Aluminum metals are well known to be difficult to solder or braze because they develop an oxide surface film which is difficult to remove or penetrate. Various soldering fluxes have been suggested to overcome this difficulty in conjunction with such methods as ultrasonic soldering, rub soldering and the like.
Alloys which are reported to have been somewhat successful in use as aluminum solders are relatively high-melting point, good tensile strength zinc alloys containing such metals as aluminum, copper, nickel, magnesium, and chromium, and lower-melting solders largely composed of tin and/or cadmium, and which contain lower amounts of zinc, usually in the range of 10-30 percent.
While there are numerous suggestions of the use of various soldering fluxes to enable a solder to wet an aluminum surface and subsequent use of the same or a different solder, the methods proposed have not made the soldering of aluminum and its alloys a chore which can be performed by the usual handyman or hobbyist. It has now been found that these materials can be soldered quickly and economically by first preparing a surface to be soldered with a zinc/lead/tin alloy and then applying a conventional lead-tin solder to the prepared surface.
2. Description of the Prior Art
Numerous prior art references have disclosed the use of zinc alloys for soldering or bracing aluminum or aluminum alloys. For example, U.S. Pat. No. 1,233,803 discloses the use of a tin-zinc alloy followed by a tin-cadmium alloy; stearic acid is used as an essential flux (not mixed with another material). The steps of the process disclosed in this patent involve (1) heating the aluminum metal to be soldered; (2) applying the flux; (3) applying the Sn--Zn alloy; (4) further heating; (5) rubbing the molten alloy with a tool; (6) reheating or continuing the prior heating; and (7) applying the second alloy (Sn--Cd).
U.S. Pat. No. 3,733,687 discloses a solder alloy containing 0.5-4.5 percent by weight aluminum, 0.1-4.0 percent by weight copper, 0.005-0.08 percent by weight magnesium, 0.0-0.5 percent by weight nickel, and 0.0-0.5 percent by weight chromium, balance zinc. This reference describes the alloy disclosed therein as suitable for soldering aluminum to aluminum or to other metals such as copper, brass or iron.
U.S. Pat. No. 3,855,679 describes a two-step soldering method for aluminum involving the use, first, of a lead/tin/silver/antimony solder, and, second, of a lead/tin solder.